Add fs package

Add diff comparison with support for double walking
two trees for comparison or single walking a diff
tree. Single walking requires further implementation
for specific mount types.

Add directory copy function which is intended to provide
fastest possible local copy of file system directories
without hardlinking.

Add test package to make creating filesystems for
test easy and comparisons deep and informative.

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

fs/hardlink.go

@@ -0,0 +1,12 @@
+package fs
+
+import "os"
+
+// GetLinkSource returns a path for the given name and
+// file info to its link source in the provided inode
+// map. If the given file name is not in the map and
+// has other links, it is added to the inode map
+// to be a source for other link locations.
+func GetLinkSource(name string, fi os.FileInfo, inodes map[uint64]string) (string, error) {
+	return getHardLink(name, fi, inodes)
+}